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synchronization processes with read & write to file c#

I am trying to stop all other processes from reading and writing to a file so I need to synchronize between process,how can I do it?
It will be helpful if someone will give me a pattern for it, and show me where should I enter the read and write section in the code.

Alright. Easy thing thought if that's your aim. You can use a filestream to open up your file. Like..
using (var stream = new FileStream(
#"C:\files\yourFile.txt",
FileMode.Open,
FileAccess.ReadWrite,
// that's the important parameter to set
// it locks the file from other processes
// as long as the stream persists
FileShare.None)) {
// give it some logic ...
}
Messed up. Didn't note the questions intention, my bad. If you try to close a process from reading/writing to a file. Try to find out which and kill it.

Empty File Content Which Used by Another Process

I have a log file of my application, I do some manipulation by sided application on the log file.
At the end of the manipulation, I want to delete the file - which is not possible becuase file is used, so I just want to empty it - delete the contents.
I tried:
using (FileStream stream = File.Open(query.FileName, FileMode.Open, FileAccess.ReadWrite, FileShare.ReadWrite))
{
using (StreamWriter writer = new StreamWriter(stream, true))
{
writer.Write("");
reader.Close();
}
}
and:
using (FileStream stream = File.Open(query.FileName, FileMode.Open, FileAccess.ReadWrite, FileShare.ReadWrite))
{
stream.SetLength(0);
stream.Close();
}
and:
System.IO.File.WriteAllText(#"path", string.Empty);
Notihg works.
How to overrride file content?

Not at all. It will crash, because file is being used by another process
Well, it probably isn't another process, it probably is yours. You'll have to do this after closing the log file. But there's a more general fix for that. Go back to the code that creates the log file and add the FileShare.Delete option.
This option allows deleting files that are in use. You can now simply use File.Delete() in your code, even if the log file is still opened. This will put the file in a "delete pending" state, anybody that tries to open it will be slapped with an access denied error. The file on the disk will automatically disappear when the last handle to the file is closed.
Yet another useful option is FileOptions.DeleteOnClose. Now it is completely automatic, the file is automatically deleted without you having to do anything at all. I can't tell which one is best in your case, you probably want to avoid deleting the log file when your program crashed so FileShare.Delete is best.

You can use the below code too
System.IO.File.WriteAllText(#"Path of your file",string.Empty);

Using MemoryMappedFile and FileSystemWatcher to detect new entries to logfile

I have a logfile that is written by a 3rd party application and I'd like my application to "read" that log file in real/near-time, parse the new log entries and act upon certain events.
My thought was that I could achieve this with a combination of FileSystemWatcher (to signal file changes) and MemoryMappedFile (to continue reading from a certain offset).
However, since this is the first time I'm using MemoryMappedFiles I do run into some issues which probably arise from not understanding the concept correctly (e.g. I'm unable to open the existing File as it's in use by the other process).
I was wondering if someone has an example of how to use MemoryMappedFiles to read a file that is locked by another process?
Thanks,
Tom
EDIT:
From the comments, it looks like Memory Mapped Files won't help me accessing files that have an exclusive lock. However, "tail" tools like, e.g. Baretail (http://www.baremetalsoft.com/baretail/index.php) are able to do just that. It has no problem reading the file that has an exclusive lock from another application in 1s intervals). So, there has to be some way to do this?
EDITEDIT:
To answer my own question, the trick in opening a locked file is, creating the FileStream with the following access flags:
fileStream = new System.IO.FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.Delete | FileShare.ReadWrite);

To answer my own question, the trick in reading a locked file is creating the FileStream with the following access flags:
FileStream fileStream = new System.IO.FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.Delete | FileShare.ReadWrite);
Now it's just a matter of either doing interval based polling or looking for FileSystemWatcher change events to detect file changes

I'm not sure if MemoryMappedFiles are going to help you. Take a look at FileStream:
var stream = new FileStream(path, FileMode.Open, FileShare.Read);
stream.Seek(offset, SeekOrigin.Begin);
Though if the 3rd-party application has the file locked exclusively, there's not much that you can do about it...

[Begin 2nd EDIT]
One more idea...
If the third party app happens to use a logging framework like NLog, log4net, or System.Diagnostics, you could still write your own Target/Appender/TraceListener and route the messages somewhere that you could look at them (such as a file that is not opened exclusively, to another process, etc).
If your third party app is using a logging framework, we probably would have heard about it by now ;-)
[End 2nd EDIT]
[Begin EDIT]
I think I misread the question. It sounded at first like you were using a third party library that had logging implemented and you wanted to do this parsing from within the program that was generating the logging. Having reread your question, it sounds like you want to "listen" to the log file from outside of the application. If that is the case, my answer probably won't help you. Sorry.
[End EDIT]
I don't have anything to offer about MemoryMappedFiles, but I wonder if you could achieve what you are after by writing a custom listener/target/appender for the 3rd party logging system?
For example, if you are using NLog, you could write a custom Target and direct all of your logging messages there (while also directing them to the "real" Target(s)). This way you get crack at each log message as it is logged (so it is actually real time, not near real time). You could do the same thing with log4net and System.Diagnostics.
Note that NLog even has a "MethodCall" target. To use that one you only have to write a static method with the correct signature. I don't know if log4net has a similar concept to this.
This seems like it would be easier to get working reliably than trying to read and parse the log file as it is being written by the third party software.

If the file is "in use", there isn't anything that can be done about that. It truly is "in use". MemoryMappedFiles are for either reading large amounts of data off the drive or sharing data with other programs. It will not help getting around the "in use" limitation.

Memorymapped files are under the same restrictions as the FileStream you initialize it with, be sure that you initialize your Memory-Mapped-File like this
var readerStream = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
var mmf = MemoryMappedFile.CreateFromFile(readerStream, null, 0, MemoryMappedFileAccess.Read, null, HandleInheritability.None, false);
If some other process have completely locked it even from writing you're in bad luck, not sure if there's a way around that. Perhaps use some timer do detect when the process has stopped writing to it.

I've done something similar just for monitoring log files on a console (as opposed to processing), but the principles are the same. Like you, I use a FileSystemWatcher, and the important logic is in my OnChanged event handler:
case WatcherChangeTypes.Changed:
{
System.IO.FileInfo fi = new FileInfo(e.FullPath);
long prevLength;
if (lastPositions.TryGetValue(e.FullPath, out prevLength))
{
using (System.IO.FileStream fs = new FileStream(
e.FullPath, FileMode.Open, FileAccess.Read))
{
fs.Seek(prevLength, SeekOrigin.Begin);
DumpNewData(fs, (int)(fi.Length - prevLength));
lastPositions[e.FullPath] = fs.Position;
}
}
else
lastPositions.Add(e.FullPath, fi.Length);
break;
}
where lastPositions is
Dictionary<string, Int64> lastPositions = new Dictionary<string, long>();
and DumpNewData is simply
private static void DumpNewData(FileStream fs, int bytesToRead)
{
byte[] bytesRead = new byte[bytesToRead];
fs.Read(bytesRead, 0, bytesToRead);
string s = System.Text.ASCIIEncoding.ASCII.GetString(bytesRead);
Console.Write(s);
}

The process cannot access the file because it is being used by another process

I am getting binary data from a SQL Server database field and am creating a document locally in a directory my application has permissions. However I am still getting the error specified in the title. I have tried numerous suggestions posted on the web including those suggested in previous posts on Stackoverflow. I have also used ProcessExplorer > Find Handle to locate the lock and it returns nothing as if the file is not locked.
I am using the code below to save the file to the file system and I then try to copy this file to a new location later in the application process within another method. It is this copy method that takes the path of the newly created file that throws the exception.
The file itself is created with its content and i can open it through Windows Explorer without any problems.
Am I missing something completely obvious? Am I creating the file correctly from the database? Any help on solving or better diagnosing the problem would be much appreciated.
// Get file from DB
FileStream fs = new FileStream(
"C:\myTempDirectory\myFile.doc", FileMode.OpenOrCreate, FileAccess.Write);
BinaryWriter br = new BinaryWriter(fs);
br.Write("BinaryDataFromDB");
fs.Flush();
fs.Close();
fs.Dispose();
// Copy file
File.Copy(sourceFileName, destinationFilename, true);

Try adding a call to GC.Collect() after you have disposed of your streams to force the garbage collector to clean up.
// Get file from DB
using(FileStream fs = new FileStream("C:\myTempDirectory\myFile.doc", FileMode.OpenOrCreate, FileAccess.Write))
using(BinaryWriter br = new BinaryWriter(fs))
{
br.Write("BinaryDataFromDB");
fs.Flush();
}
//Force clean up
GC.Collect();
// Copy file
File.Copy(sourceFileName, destinationFilename, true);

change your code as follows, the problem is that the the filestream isn't being garbage collected when you need it to:
// Get file from DB
using (FileStream fs = new FileStream("C:\myTempDirectory\myFile.doc", FileMode.OpenOrCreate, FileAccess.Write))
{
BinaryWriter br = new BinaryWriter(fs);
br.Write("BinaryDataFromDB");
fs.Flush();
fs.Close();
}
// Copy file
File.Copy(sourceFileName, destinationFilename, true);

What about using?
string source = #"C:\myTempDirectory\myFile.doc";
using(FileStream fs = new FileStream(
source, FileMode.OpenOrCreate, FileAccess.Write, FileShare.Read))
{
BinaryWriter br = new BinaryWriter(fs);
br.Write("BinaryDataFromDB");
}
File.Copy(sourceFileName, destinationFilename, true);
EDIT: Try to inform a FileShare.Read permission.

I came to understand that though the error debugger says that the error lies in this code.. But that isn't where the error is..
I faced a similar issue and I came with this solution.. consider all the posts above..
May be it may help some one..
I used the Image to show it in a picturebox after retreiving from Database and saving it as "temp.bmp" using normal coding without using "using" keyword using this code at first:
PictureBox1.Image = Image.FromFile("temp.bmp");
and it raised and error and I really didn't got head and tail of the error.. and so I came up with this solution.
Instead of assigning it directly try this code:
Bitmap img;
using (Bitmap bmp = new Bitmap("temp.bmp"))
{
img = new Bitmap(bmp);
}
pictureBox1.Image = img;
coming to the filestream part I just used normal code as follows:
FileStream fs = new FileStream("filepath",FileMode.Create);
and it worked like a piece of cake
It really helped

Is it that Filestream and BinaryWriter cannot be used at the same time? For instance, a streamwriter and a streamreader cannot both be called on the same file. However, this doesn't make sense, as far as I know, it should not in this case. Perhaps try closing br as well?

Try disposing your BinaryWriter object before doing the copy.

Is there a background process such as antivirus or file-system indexing locking the file just long enough to cause problems with your application? Try pausing for 3 seconds to see if your problem disappears.
using System.Threading;
fs.Dispose();
Thread.Sleep(3000);
// Copy file

This was what I did:
Stream stream = new MemoryStream();
var tempStream = new FileStream(pathToFile, FileMode.Open);
tempStream.CopyTo(stream);
tempStream.Close();
then use stream object wherever you want.

I seem to encounter this only after I have published an application. If you close the message box and try again to debug, nothing will happen.
MS Help says to get all the way out of Visual Studio and restart it. Its easier to bring up Task manager and end the process. Its name will be the solution name followed by ".vshost" (e.g. project name: PLC.sln; process name: PLC.vshost.exe). The process will restart automatically. In Windows 7 one could usually see something happen when ending a process. But in 10 the Task Manager window rarely changes.
I get this message when I try testing a program after changing code. Apparently the .exe is not closed when one stops debugging and the error occurs when VS tries to write a newly complied exe file. I sometimes have to end the process twice to keep the error message from coming back. (I have to encounter the error twice; ending the process twice and then rerunning doesn't help.)
This is a bug in Visual Studio.

In C#, if 2 processes are reading and writing to the same file, what is the best way to avoid process locking exceptions?

With the following file reading code:
using (FileStream fileStream = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.None))
{
using (TextReader tr = new StreamReader(fileStream))
{
string fileContents = tr.ReadToEnd();
}
}
And the following file write code:
using (TextWriter tw = new StreamWriter(fileName))
{
tw.Write(fileContents);
tw.Close();
}
The following exception details are seen:
The process cannot access the file
'c:\temp\myfile.txt' because it is
being used by another process.
What is the best way of avoiding this? Does the reader need to retry upon receipt of the exception or is there some better way?
Note that the reader process is using a FileSystemWatcher to know when the file has changed.
Also note that, in this instance, I'm not looking for alternatives ways of sharing strings between the 2 processes.

You can open a file for writing and only lock write access, thereby allowing others to still read the file.
For example,
using (FileStream stream = new FileStream(#"C:\Myfile.txt", FileMode.Open, FileAccess.ReadWrite, FileShare.Read))
{
// Do your writing here.
}
Other file access just opens the file for reading and not writing, and allows readwrite sharing.
using (FileStream stream = new FileStream(#"C:\Myfile.txt", FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
{
// Does reading here.
}
If you want to ensure that readers will always read an up-to-date file, you will either need to use a locking file that indicates someone is writing to the file (though you may get a race condition if not carefully implemented) or make sure you block write-sharing when opening to read and handle the exception so you can try again until you get exclusive access.

If you create a named Mutex you can define the mutex in the writing application, and have the reading application wait until the mutex is released.
So in the notification process that is currently working with the FileSystemWatcher, simply check to see if you need to wait for the mutex, if you do, it will wait, then process.
Here is a VB example of a Mutex like this that I found, it should be easy enough to convert to C#.

Get your process to check the status of the file if it is being written to. You can do this by the presence of a lock file (i.e. the presence of this other file, which can be empty, prevents writing to the main file).
Even this is not failsafe however, as the two processes may create the lock file at the same time - but you can check for this before you commit the write.
If your process encounters a lock file then get it to simply sleep/wait and try again at a predefined interval in the future.

Is there any particular reason for opening the file with FileShare.None? That'll prevent the file from being opened by any other process.
FileShare.Write or FileShare.ReadWrite should allow the other process (subject to permissions) to open and write to the file while you are reading it, however you'll have to watch for the file changing underneath you while you read it - simply buffering the contents upon opening may help here.
All of these answers, however, are equally valid - the best solution depends on exactly what you're trying to do with the file: if it's important to read it while guaranteeing it doesn't change, then lock it and handle the subsequent exception in your writing code; if it's important to read and write to it at the same time, then change the FileShare constant.

You can use a Mutex object for this.

The reader and writer both need retry mechanisms. Also FileShare should be set to FileShare.read for the readers and FileShare.none for the writer. This should ensure that the readers don't read the file while writing is in progress.
The reader (excluding retry) becomes
using (FileStream fileStream = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.Read))
{
using (TextReader tr = new StreamReader(fileStream))
{
string fileContents = tr.ReadToEnd();
}
}
The writer (excluding retry) becomes:
FileStream fileStream = new FileStream(fileName, FileMode.Create, FileAccess.Write, FileShare.None);
using (TextWriter tw = new StreamWriter(fileStream))
{
tw.Write(fileContents);
tw.Close();
}

Write to a temp file, when finished writing rename/move the file to the location and/or name that the reader is looking for.

The best thing to do, is to put an application protocol on top of a file transfer/ownership transfer mechanism. The "lock-file" mechanism is an old UNIX hack that has been around for ages. The best thing to do, is to just "hand" the file over to the reader. There are lots of ways to do this. You can create the file with a random file name, and then "give" that name to the reader. That would allow the writer to asynchronously write another file. Think of how the "web page" works. A web page has a "link" to more information in it, for images, scripts, external content etc. The server hands you that page, because it's a coherent view of the "resource" you want. Your browser then goes and gets the appropriate content, based on what the page description (the HTML file or other returned content), and then transfers what it needs.
This is the most resilient type of "sharing" mechanism to use. Write the file, share the name, move to the next file. The "sharing the name" part, is the atomic hand off that makes sure that both parties (the reader and the writer) agree that the content is "complete."